The present invention relates to a plain paper copier, plain paper facsimile apparatus, printer or similar electrophotographic recording apparatus.
An electrophotographic recording apparatus includes a developing unit having a construction taught in, e.g., Japanese Patent Laid-Open Publication No. 6-175477. The developing unit has a casing storing a single-ingredient type developer, i.e., toner having high electric resistance. First toner conveying means in the form of a roller is disposed in the casing and receives the toner from a toner supply roller. The toner is magnetically deposited on the conveying means. Second toner conveying means implemented as an elastic roller intervenes between the first toner conveying means and a photoconductive drum or image carrier. The toner is electrically transferred from the first conveying means to the second conveying means. Toner particles charged to the polarity opposite to the expected or regular polarity are prevented from being transferred from the first conveying means to the second conveying means. This allows the second conveying means to deposit only the toner of regular polarity on a latent image electrostatically formed on the drum.
While the development of the latent image is not under way, the absence of the toner on the second conveying means does not matter at all in respect of the image forming process. However, if the toner is present on the second conveying means or similar member contacting the drum, then it is likely to easily deposit on the drum, compared to the case wherein it is absent. As a result, not only the toner is wastefully consumed, but also the resulting image has its background contaminated.
Further, assume that image transferring means for transferring the toner image from the drum to a sheet is of the type contacting the drum. Then, if the charge of the toner existing on the drum is unstable, it is likely that the toner is transferred from the drum to the image transferring means. This part of the toner smears the rear of a sheet.